If there is a temperature difference between both ends of a solid material, a concentration difference of carriers (electrons or holes) having thermal dependence occurs, leading to an electric phenomenon called a thermal electromotive force, that is, a thermoelectric effect. As such, the thermoelectric effect means a reversible and direct energy conversion between a temperature difference and an electric voltage. The thermoelectric effect may be classified into thermoelectric power generation that produces electric energy and thermoelectric cooling/heating that causes a temperature difference between both ends by electricity supply.
A thermoelectric material showing the thermoelectric effect, that is, a thermoelectric semiconductor has been much studied due to its eco-friendliness and sustainability during power generation and cooling. Moreover, since the thermoelectric material is capable of directly producing power from industrial waste heat, vehicle waste heat, etc., and thus is useful for improving fuel efficiency or reducing CO2, etc., the thermoelectric material has attracted more and more attention.
A thermoelectric module has, as a basic unit, one pair of p-n thermoelectric elements including a p-type thermoelectric element (TE) in which holes move to transfer thermal energy and an n-type TE in which electrons move to transfer thermal energy. The thermoelectric module may include an electrode that connects the p-type TE with the n-type TE.
For a conventional thermoelectric module, soldering has been widely used to bond an electrode with thermoelectric element. Conventionally, the electrode and the thermoelectric element are generally bonded using, for example, an Sn-based solder paste or a Pb-based solder paste.
However, such a solder paste has a limitation in driving a thermoelectric module in a high-temperature condition because of its low melting point. For example, a thermoelectric module using an Sn-based solder paste to bond a thermoelectric element and an electrode is difficult to drive at a temperature over 200° C. A thermoelectric module using an Pb-based solder paste is difficult to drive at a temperature over 300° C.